1. Field of the Invention
The present invention is generally related to complementary targets for use in conjunction with a magnetically sensitive component and, more particularly, an engine shaft that is machined to define first and second radially enlarged integral portions of the shaft which are shaped to define complementary target regions.
2. Description of the Prior Art
Many different types of geartooth sensors are known to those skilled in the art. Some geartooth sensors utilize a Hall effect element associated with a permanent biasing magnet. Others incorporate a magnetoresistive element, such as permalloy, combined with a permanent magnet that provides a biasing field. In certain applications, a single rotatable target, comprising a plurality of teeth and interstitial slots is used in conjunction with a geartooth sensor. One disadvantage of many single target geartooth sensors is that the device senses changes in a magnetic field and is unable to accurately determine whether a tooth or a slot is proximate the sensor upon start up. In order to overcome this deficiency, some geartooth sensor incorporate two rotatable targets, wherein each target comprises a plurality of teeth and slots. It is particularly advantageous if the two targets are complementary in nature. Throughout this description, targets are described as being complementary if the teeth of one target are disposed in circumferential alignment with the slots of the other target and vice versa. In an arrangement of this type, the complementary targets affect the geartooth sensor in opposite ways so that the tooth of one target distorts the magnetic field of the biasing magnet in a particular way which is generally opposite to the distortion when the tooth of the other target moves into a position proximate the sensor. This complementary nature of the targets permits power up recognition capability and also facilitates the accurate determination of the angular position of a shaft to which the complementary targets are attached.
U.S. Pat. No. 4,789,826, which issued to Willett on Dec. 6, 1988, discloses a system for sensing the angular position of a rotatable member using a Hall effect transducer. The angular position of the member, such as the shaft of a tension arm assembly, is sensed by the combination of a circular type of magnet secured to the rotatable member and selectively polarized relative to its diameter to define a magnetic north-south pole pair and a stationary Hall effect transducing device secured in close and constant proximity to the ring magnet. In a preferred embodiment of this device, the Hall effect transducing device is located in the region of a magnetic null of the field generated by the magnetic poles when the rotatable member is in a selected angular position.
U.S. Pat. No. 4,785,242, which issued to Vaidya et al on Nov. 15, 1988, discloses a position detecting apparatus which uses multiple magnetic sensors for determining relative and absolute angular position of a rotating shaft. A position detecting apparatus utilizes a first magnetic sensing device for accurately determining the angular position of a rotor and a second magnetic sensing device for absolutely determining the angular position of the rotor. The first sensing device includes a first target operatively associated with the rotor so as to rotate therewith and also includes a first sensor disposed at a fixed distance from the first target independent of the absolute angular position of the rotor to define a first air gap therebetween and a first magnet is disposed in proximity to the first target and the first sensor to create a first magnetic field in the first air gap.
U.S. Pat. No. 4,506,217, which issued to Rothley et al on Mar. 19, 1985, describes a geartooth position and speed sensor with four bridge circuit connected magnetic resistance tracks. Four meander-arranged permalloy resistance tracks are located on a substrate at the corners of a rectangle. They are spaced in a circumferential direction by approximately half of the pitch distance of the teeth of a starter gear. The resistances are connected together in a voltage divider configuration or in the form of a bridge circuit supplied from a constant current source.
U.S. Pat. No. 4,570,118, which issued to Tomczak et al on Feb. 11, 1986, discloses an angular position transducer which includes permanent magnets and a Hall effect device. The transducer for creating an electrical signal proportional to the angular position of a member pivotably mounted on a given axis includes an element that is pivoted directly by the member and contains a means for creating a flux field linearly varying in intensity along a given operating line extending in an air gap between spaced portions and having a preselected arcuate shape. A linear Hall effect device, with an output voltage proportional to the intensity of the flux field in which the device is exposed, is mounted at a fixed position on the operating line and in the air gap. Consequently, as the element is pivoted by the monitored member, the output voltage from the Hall effect device varies proportionally to the position of the Hall effect device along the operating line.
U.S. Pat. No. 5,041,784, which issued to Griebeler on Aug. 20, 1994, describes a magnetic sensor with a rectangular field distorting flux bar. The sensor is for use in measuring the position, velocity or direction of movement of an object having alternating zones of magnetic conductivity with a permanent magnet member having a pole face facing the moving object and having an axis transverse to the direction of movement thereof. A ferromagnetic strip of high permeability is mounted on the face of the magnet coaxial therewith having a length dimension in the direction of movement of the object greater than the width dimension transversed to the direction of movement. The ferromagnetic strip distorts the field of the permanent magnet member in the area of a pair of the sensor elements such that the flux lines in the area of each of the sensors are urged toward a transverse direction relative to the direction of movement of the object, whereby the flux field in the area of each of the sensors is uniform.
In patent application Ser. No. 08/099,296, which was filed by Wu on Jul. 29, 1993 and assigned to the assignee of the present application, a magnetoresistive element is used in conjunction with a complementary target arrangement in order to provide power up recognition in an angular position sensor. FIGS. 2A and 2B, which will be described in greater detail below, illustrate this arrangement which comprises two rotatable targets that are spaced apart from each other to define a gap therebetween. The rotatable targets are suitable for attachment to a shaft so that they rotate about a central axis in coordination with the shaft. The application of the magnetoresistive geartooth sensor permits the angular position of the shaft to be monitored. As the two rotatable targets rotate about the central axis, a tooth of one target passes the magnetoresistive sensing element simultaneously with a slot of the other target and vice versa. This coordinated movement of the teeth of one target with the slots of the other target advantageously distorts the magnetic field of a biasing magnet to facilitate the accurate determination of the position of both rotatable targets. The teeth provide ferromagnetic segments which distort the magnetic field and permit the magnetoresistive element to detect the movement of the targets. Patent application Ser. No. 08/099,296 is hereby explicitly incorporated by reference in this application.
Although the geartooth sensors described above provide a means for monitoring the angular position of a rotatable shaft, they possess a disadvantage in certain applications. The rotatable targets are individually machineable to define the teeth and slots and are subsequently attachable to each other and to the shaft in order that rotation of the shaft will be coordinated with rotation of the two targets. However, in certain applications, it is disadvantageous to require the individual manufacture of the targets and the additional operation of attaching the targets together and to the shaft. It would therefore be economically beneficial if a complementary target could be manufactured as an integral part of the rotatable shaft.